Known friction clutches provide a releasable torsional connection between a motor vehicle engine flywheel and an associated transmission. Repeated clutch disengagement and engagement cycles wear the friction material of the clutch driven disc. The wear results in a change in the axial location of the pressure plate in the engaged position. The shift in axial location results in a progressive decrease of the clutch engagement force or clamping load. Clutches are commonly provided with adjustment mechanisms to compensate for such wear.
The clutch clamping load is generated by a spring acting directly or indirectly against the pressure plate and reacting directly or indirectly against the clutch cover.
One type of spring configuration commonly employed is a diaphragm spring having an annular portion with radially inwardly directed fingers extending from the annular portion. The radially innermost tips of the fingers engage a release assembly. The fingers bow with a movement of the tips to deflect the annular portion, and thereby release the clutch, when the release assembly is axially displaced.
As the friction material wears, the engaged position of the finger tips, and the release assembly, move closer to the flywheel. Adjustment mechanisms disposed between the cover and the levers or between the pressure plate and the diaphragm spring compensate for this change.
One type of known adjustment mechanism relies on the relative rotation of two annular cams, each having inclined cam surfaces in engagement with each other. The relative rotation of the cams compensates for wear of the friction material. The cams are biased to rotate in a direction that increases a combined height or thickness of the cams. A rotative biasing force is induced by a torsional biasing spring functionally disposed between the two cams. A number of different spring configurations can be employed in this capacity, including coil tension springs, torsional round wire springs, and torsional flat wire springs.
It is also known to provide adjustment limiting devices which prevent the cams from overadjusting when the release bearing is moved too far. One such device relies on the use of pins frictionally engaged with the pressure plate to limit cam adjustment. However, such a mechanism relies on establishing a precise frictional relationship between the pins and the pressure plate to provide the desired adjustment limitation without interfering with the operation of the clutch. Further, the frictionally retained pins contribute to a reduction in the clamping load transferred to the friction material by the pressure plate.
It is desired to provide a mechanism for limiting the relative rotation of the cams which does not rely on overcoming a frictional relationship between the pressure plate and pins disposed therein.